Best IR filters to use with RED MX

I'm about to work on a production using the RED MX. The DP had originally requested combination IRND's but the rental house has been unable to provide these and offered the Tiffen T1 as a good alternative. I've had past experience with the Schneider True-Cut IR hot mirror with the Red and only using it in conjunction with ND.6 or higher. I've been told the Tiffen T1 is better and should be left in all the time even when not using ND. The DP has concerns about this though. I'd really appreciate if anybody can offer advice on the matter! Cheers

Just found this:
"The Red One Mysterium X has an internal low-pass filter. This will block out infrared light for about 4 to 5 stops. So you don’t need to add a Hot Mirror or IR filter unless your ND is greater than 1.2 or so."
Is this true!!?
Thanks

IR and Far-Red filtration is something of a vexed issue at present, with each new digital camera that comes out having a different level of in-built filtration. I understand Tiffen and Schneider are both struggling to meet the new demand for IR and IRND filters, and to provide variations on where in the spectrum they cut in. It doesn't help that while the cameras are getting more sensitive, everyone seems to want to shoot wide open to get a shallow DOF, so they stack NDs. Colour shifts, IR and Far-Red pollution, synthetic materials registering as different colours, and each camera reacting differently - it's a minefield!

By my limited understanding, the Tiffen T1 is a Far-Red filter (680 - 720nm). It was not designed for the RED MX, but for cameras with narrower spectrum internal filters that allow through a certain range of Far-Red, such as Alexa and the various Sonys.

I'm not at all familiar with REDs, but from what I've read I believe the Hot Mirror is a more appropriate IR filter: